Resistive devices are well known in the art. Resistors typically comprise a resistive material, such as a thick film resistor element or a resistive wire, to which terminations are attached for electrically coupling the resistor to other circuit elements. One type of resistor is a variable resistor for varying the resistance provided between the terminations. This variable resistance can be utilized in a number of applications, such as in volume controls for stereos and dimmers for lighting purposes.
Variable resistors are typically manufactured in a configuration in which a resistive element is terminated in at least one fixed terminal. A moveable terminal is attached to an actuator, such as a rotary knob, thumbwheel, or slideable member, such that the moveable terminal contacts different regions of the resistive element as a user manipulates the actuator. In this manner, the resistance between the fixed terminal and the moveable terminal varies as the actuator is manipulated.
More specifically, in one conventional variable resistor utilizing a thumbwheel, an insulating substrate is imprinted with a resistor network. The substrate and a cover form a housing containing the thumbwheel, terminals embedded in the cover, and conductors carried by the thumbwheel which selectively connect portions of the resistor circuit to the terminals such that the resistance between the terminals is determined by the thumbwheel position.
As can be seen from the above description, conventional variable resistors utilize a relatively large number of parts, e.g., actuator, cover, terminals, conductors, substrate, and resistor network. During manufacturing of the variable resistor, these parts must be cataloged, ordered, and stocked separately. Additionally, the parts must be assembled in labor intensive processes involving the use of fasteners such as screws, pins, or rivets for fastening the actuator to the terminals. Once the variable resistor is assembled, wear and tear can occur which can interrupt the operation of the resistor. For instance, in variable resistors having a terminal which slides across a resistive element, the resistive element and/or the terminal can become worn after repeated use. If the terminal is very small or fragile, as in smaller variable resistors, it can even break entirely from the forces applied thereto by the actuator and the resistive element.
Thus, what is needed is a variable resistor which includes a relatively small number of parts that can be easily assembled. Furthermore, parts included in the variable resistor should not become worn with repeated use.